Fig. REF  compares the goodputs of the proposed scheme and five baseline schemes. It is obviously observed that the proposed scheme performs much better than the five baseline schemes in high SNR regime. However, as opposed to both the OMA and virtual MIMO schemes, the superior performance of the proposed scheme cannot be perfectly exhibited at low SNR. This is due to the fact that the significant advantages of NOMA are based on the premise of high SNR[1]}. Whereas, this result no longer holds at low SNR. It is worth noting that the condition of high SNR is commonly satisfied to achieve a very low outage (e.g., \(10^{-5}\) ) in 5G systems [2]}. For instance, by considering a carrier bandwidth of 100MHz, thermal noise level of -174dBm/Hz and maximum output power budget of 24dBm, the transmit SNR is calculated as 118dB [3]}. It is also observed from Fig. REF  that the proposed scheme generally outperforms the NOMA scheme in terms of the goodput. For example, by aiming at \(T_g=6\) bps/Hz, the required transmit SNRs for the proposed scheme and NOMA scheme must be set as 65dB and 77dB, respectively. Henceforth, the introduction of the virtual MIMO yields a reduction of the transmit SNR by 12dB, which remarkably conserves energy with guaranteed QoS for IoT networks. In addition, it is shown that the proposed scheme is a little bit inferior to the NOMA scheme under low SNR because of the negative effect of antenna correlations. The similar observations can be found coincidentally between the OMA and virtual MIMO schemes. Besides, it can be seen that both hybrid MA-based schemes achieve a higher goodput than the proposed scheme at low SNR. Nevertheless, the maximum achievable goodput of the hybrid MA scheme in [4]} is tremendously restricted. In contrast, the virtual MIMO-hybrid MA scheme is able to strike a balance between boosting spectral efficiency and reducing system overhead for resource-limited IoT networks.
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